Human milk‐sharing practices and infant‐feeding behaviours: A comparison of donors and recipients

Abstract Human milk sharing (HMS) is growing in popularity as an infant‐feeding strategy in the United States. HMS families are a hidden population because HMS is a nonnormative and stigmatized behaviour. Thus, gaining access to HMS participants is challenging, and research on this topic remains limited. In particular, little is known about the broader infant‐feeding behaviours of HMS parents. This study aimed to describe and compare the infant‐feeding behaviours and HMS practices among a network of HMS donors and recipients. A detailed online survey was distributed to HMS parents in the Washington, DC region. Bivariate analyses were used to summarize the data by donor/recipient status when possible. Group differences were tested using analysis of variance for continuous variables and χ 2 tests for categorical variables. Donors and recipients did not differ in their sociodemographic characteristics. Recipients were significantly more likely than donors to have experienced complications of labour and delivery, traumatic birth, postpartum depression or a negative breastfeeding experience. Donors and recipients did not differ significantly in their duration of lactation or HM‐feeding. Interestingly, 30% of recipients ever produced excess milk and 21% of donors ever had difficulty producing enough milk for their child. Compared with donors, recipients faced numerous maternal health challenges, but were still able to achieve a long duration of HM‐feeding. HMS recipients represent a vulnerable group who may benefit from additional psychosocial and lactation support to improve their health and breastfeeding outcomes. Additional research is needed to investigate the associations between HMS participation, infant‐feeding behaviours and lactation outcomes.

Public health and medical authorities recommend that infants be exclusively breastfed for 6 months, with continued breastfeeding for 1 year or longer (Eidelman, 2012;Gartner et al., 2005;Kramer & Kakuma, 2012;Martens, 2012). However, many American women fall short of meeting those goals (Prevention, 2020) and, thus, rely on various supplemental feeding strategies to feed their infants. HM sharing (HMS) has recently emerged as one such supplemental infant-feeding strategy. This study defines HMS as the commercefree exchange of HM between individuals for infant feeding that occurs outside of the formal milk banking system. HMS is sometimes referred to as peer to peer or informal because it relies on the individual participants to negotiate the specific terms of the exchange (A. E. L. Palmquist et al., 2019). It is important to note that this phenomenon is distinct from HM selling, which is also done peer to peer, but includes a financial transaction. HMS is a contemporary transformation of historical allonursing-one that still relies on a donor with surplus milk and a recipient with a milk deficiency, but is no longer limited by temporality and geographic proximity because of the modern inventions of refrigeration, the internet and the doubleelectric breast pump.
Contemporary HMS has been largely enabled by the ready availability of surplus expressed HM (E-HM). In the industrialized, high-income populations where HMS has been studied, mothers rely substantially on HM expression to feed their own infants (Boswell-Penc & Boyer, 2007;Labiner-Wolfe et al., 2008). This has created an environment ripe for HM exchange, where some women are unable to produce enough milk to feed their infants and others produce in -married, healthy, White, well-educated and financially secure (Osbaldiston & Mingle, 2007). HMS recipients are often mothers with a strong desire to breastfeed, but who experience breastfeeding challenges and lactation insufficiency (Cassar-Uhl & Liberatos, 2018; McCloskey & Karandikar, 2019; A. E. Palmquist & Doehler, 2014;Perrin et al., 2014;Tomori et al., 2016). Parents whose infants are experiencing inadequate growth or are intolerant of infant formula are another important subgroup of HMS recipients (Cassar-Uhl & Liberatos, 2018;McCloskey & Karandikar, 2018;O'Sullivan et al., 2018;A. E. Palmquist & Doehler, 2014).
The self-regulated and peer-to-peer nature of HMS renders it a highly individualized and heterogeneous set of practices. Prior research has shown that much of HMS is facilitated through the internet, where donors and recipients connect using Facebook groups and milk-sharing websites (Akre et al., 2011;Keim et al., 2014;O'Sullivan et al., 2018;A. E. Palmquist & Doehler, 2014;Perrin et al., 2014;Palmquist & Doehler, 2015). Less is known about milk sharing that operates at a local level among friends, family and community members. Some HMS recipients rely on one or two long-term donors, while others receive S-HM from many different donors (Gribble, 2014;A. E. Palmquist & Doehler, 2014;Reyes-Foster et al., 2015;Thorley, 2008). An important area of interest to specialists in maternal and child nutrition is learning how S-HM is incorporated into the overall infant-feeding strategies of HMS families.
This remains an under-researched topic within the HMS literature.
HMS has generated significant controversy because of the potential risks involved and the "yuk factor," as the notion of feeding one woman's milk to another's child may generate feelings of disgust or aversion (Shaw, 2004(Shaw, , 2007. Microbial and viral pathogens can be transmitted in HM (Ando et al., 2004;Bardanzellu et al., 2018;Bowen et al., 2017;Josephson et al., 2014;Sosa & Barness, 1987). HM can also be contaminated with a prescription or recreational drugs, or altered by suboptimal practices during expression or storage that could lead to microbial contamination or loss of nutrients (Burra et al., 2019;Datta et al., 2019;Eglash et al., 2017;Fierro et al., 2019;Hamosh et al., 1996Hamosh et al., , 1997. Given these potential risks, numerous organizations, including the US Food and Drug Administration and HMBANA, have released statements cautioning against HMS and positioning it as a high-risk behaviour (HMBANA & European Milk Bank Association, 2015;United States Food and Drug Administration, 2015). Yet, the common alternative to maternal milk, infant formula, also has numerous risks associated with it, and mothers are

Key messages
• All human milk sharing (HMS) participants achieved a long duration of HM-feeding, reflecting a high value placed on HM and a strong commitment to HM-feeding.
• Recipients in this sample were largely using HMS as a strategy to supplement the mother's own milk.
• Approximately one-third of recipients ever produced more HM than needed and one-fifth of donors ever had difficulty producing enough milk, suggesting that both donors and recipients experienced breastfeeding challenges.
• Many HMS recipients encountered compounded maternal medical and mental health challenges and would therefore benefit from additional psychosocial and lactation support to improve their mental health and breastfeeding outcomes. keenly aware of these risks (Gribble, 2012). It is within this fraught context that the practice of milk sharing has continued, underscoring the strong demand for HM (Akre et al., 2011;Keim et al., 2014;O'Sullivan et al., 2018) and highlighting the importance of expanding research on this increasingly prevalent infant-feeding strategy. Gaps in the HMS scientific literature are numerous because this study is still in its infancy.
The primary objective of this study was to describe the infantfeeding behaviours and HMS practices among a geographically defined network of milk-sharing parents in the greater Washington, DC metropolitan region. In addition, we aimed to identify differences between donors and recipients in their maternal health characteristics, infant-feeding behaviours and HMS practices.

| Setting
This study used a cross-sectional web-based survey. The study was conducted during July 2019-May 2020 in the greater Washington, DC metropolitan region (DMV, which comprises the District of Columbia and parts of Maryland and northern Virginia). According to the 2020 US Census, the DMV region has an estimated total population of 6.4 million and is a highly affluent and well-educated population (Hess, 2018;Martin, 2019). According to the most recently available data, 88% of infants born in the District of Columbia in 2017 were ever breastfed, 65% were still breastfeeding at 6 months and 24% were exclusively breastfed for 6 months (Centers for Disease Control and Prevention, 2020).
Human Milk 4 Human Babies and Eats on Feets are the two primary organizations that facilitate the bulk of online HMS by hosting regionspecific Facebook groups, providing fora for donors and recipients to connect. The DMV region has two active Human Milk 4 Human Babies Facebook groups, with just over 22,000 cumulative followers, and three active Eats on Feets Facebook groups, with approximately 7200 cumulative followers. These groups are highly active, suggesting a robust network of HMS parents in the DMV region.

| Sample
Convenience sampling was used to reach members of the target population of milk-sharing parents in the DMV region. Study inclusion criteria were as follows: aged 18 years or older, Englishspeaking, had engaged in milk sharing in the past 18 months (as a donor or recipient) and lived or worked in the DMV region at the time of milk sharing. Parents were recruited through a variety of convenience sampling techniques, namely, posting advertisements on local milk-sharing websites and parenting listservs, sharing recruitment materials with local birth workers (lactation consultants, doulas and midwives) to share with their clients and snowball sampling.

| Measurement
The survey questionnaire was informed by the findings of a previously conducted ethnographic study with HMS recipients (Peregoy, 2021). Those semistructured interviews with HMS recipients provided detailed information about how HMS is organized and practiced. This information was used to develop broad content themes and guide the design of the questions and response choices.
The survey tool was reviewed for content by research colleagues and validated by members of the target population. The validation study (n = 11) used cognitive interviewing to assess construct validity and to refine the survey questions for improved clarity and validity.
Finally, usability testing (n = 8) was conducted to identify and correct issues with the web-based version of the survey before commencing data collection. The study team made real-time modifications to the survey during the validation study and usability testing in an iterative process of fine-tuning and improvement.

| Data collection
The online survey link was distributed through the various channels described above. Parents interested in participating first completed a brief screening questionnaire to ascertain eligibility. Eligible respondents were then provided with the informed consent script, which they had to read and consent to proceed with the survey. Among respondents, the mean survey completion time was 37 min. Within 48 h of survey completion, all eligible respondents received a participation incentive in the form of a $20 Amazon gift card. The convenience sampling yielded 168 respondents, 58% donors and 42% recipients.

| Data analysis
All data cleaning, recoding and analyses were performed using SAS Studio version 9.04. Bivariate analysis of sociodemographic factors, infant-feeding behaviours and HMS practices was conducted by donor/ recipient (D/R) status for all survey items asked of both donors and recipients. Differences by D/R status in continuous variables were tested using analysis of variance and in categorical measures using χ 2 tests or Fisher's exact tests for small cell sizes. For nonnormally distributed variables, data were reported as medians with interquartile range and significance testing was conducted using Wilcoxon's rank test.

| Sample characteristics
Nearly all respondents self-identified as women (Table 1). Sex data were not available. Therefore, female gender pronouns will be used in describing this sample. Donors and recipients did not differ in their sociodemographic profiles. However, the age distribution of T A B L E 1 Sociodemographic characteristics of the study participants (n = 168), stratified by HMS donor/recipient status

| Breastfeeding experience and infant-feeding behaviours
Respondents were asked a series of questions about their breastfeeding experience. Among respondents who were no longer feeding their children HM (n = 58), the median duration of HM feeding did not differ significantly between donors (13.5 months, IQR: 10.5-19.0) and recipients (12.0 months, IQR: 9.0-13.0; p = 0.1334) ( Figure 1). In their lifetime of lactation experience, recipients were less likely than donors to have ever produced more milk than needed by their child (p < 0.0001) and more likely to have ever had difficulty producing enough milk for their child (p < 0.0001), been diagnosed with a health problem affecting lactation (p < 0.05) or to have fed infant formula to their child (p < 0.05) (Table 3). Overall, 29% of respondents reported that they had ever exclusively pumped to feed their child (which did not differ significantly by D/R status).
Interestingly, 30% of recipients ever produced more HM than they needed and 21% of donors ever had difficulty producing enough milk for their child. Nearly half of the donors rated their most recent breastfeeding experience as very positive, while recipients were significantly more likely to rate their most recent breastfeeding experience negatively (29%; p < 0.05).

| Milk-sharing practices
Very few respondents had ever sold (0.6%) or purchased (2.4%) HM ( infants were still consuming their mother's own milk and 71% were still feeding at their mother's breast during part or all of the HMS arrangement. The estimated total volume of S-HM exchanged did not differ by D/R status (Supporting Information: Figure 1). Fifty-five percent of respondents exchanged a total of less than 250 ounces of S-HM, while 22% exchanged 1000 or more ounces.

| DISCUSSION
This study makes an important contribution to the literature by describing in detail the HMS practices and infant-feeding behaviours among a network of HMS parents in a large American metropolitan region. We found that all HMS participants achieved a long duration of HM-feeding and used a variety of infant-feeding behaviours, including at-the-breast feeding, formula feeding, milk sharing and exclusive pumping. We also found that, although donors and recipients did not differ in sociodemographic characteristics, they differed in their maternal experiences and some infant-feeding behaviours.
Although efforts were made to recruit a diverse sample by ethnicity, socioeconomic status and milk sharing type (online vs. issues, recipients were able to achieve a duration of HM feeding that did not differ significantly from donors. It is likely that receiving S-HM was an important strategy that helped them to achieve their HM-feeding goals. Another interesting finding is that 21% of donors ever had difficulty producing enough milk and 30% of recipients ever produced more milk than needed. Furthermore, 20% of HMS recipients had also donated their milk in the last 18 months. These findings suggest that both recipients and donors experienced challenges during their breastfeeding journeys, underscoring the complexity and mutable nature of the breastfeeding journey. Women may serve as both donors and recipients during a given lactation period, implying the potential for crossover between donor and recipient status, as supported by previous research findings ( Reyes-Foster et al., 2015). These findings suggest that donor/recipient status is transient, with more nuance and complexity to the HMS experience than previously assumed by the research community.
Additional research is warranted to investigate the role that perceived lactation insufficiency plays in milk sharing.
A higher proportion of our respondents had exclusively pumped (28.8%) than was reported in another US population (6.9%) (Keim et al., 2017). It seems logical that exclusive pumping is a common behaviour among this population, given that contemporary HMS requires a steady supply of surplus E-HM, which is enabled by the use of breast pumps. It is relatively easy to appreciate why a mother who is experiencing breastfeeding challenges-latch issues, in particular-might turn to exclusive pumping to feed her infant and then to receiving S-HM. However, the proportion of donor mothers who have exclusively pumped was not significantly lower and the motivations are less obvious for this group. It is likely that some HMS donors use exclusive pumping as a strategy to manage excessive supply, a phenomenon that has been documented in previous research (Gribble, 2014). Further research is warranted to understand the role that exclusive pumping plays in HMS, as well as the reasons F I G U R E 1 Comparison of the duration of the most recent lactation and duration of human milk (HM) feeding (months) of the youngest child among HM-sharing donors and recipients who are no longer feeding HM to their children (n = 58). The boxes represent the interquartile range containing the central 50% of values; the lines across the box represent the median values; the circles in the box represent the mean values; the whiskers represent the "minimum" (Q1 − 1.5 × IQR) and "maximum" (Q3 + 1.5 × IQR); and the circles represent outliers.
| 7 of 13 why parents turn to exclusive pumping, another breastfeeding topic with a paucity of data.
The finding that one-third of recipients' infants had been diagnosed with tongue/lip tie is notable, as this is substantially higher than the reported prevalence range among the general population of infants (4%-10%) (Hill et al., 2021;Segal et al., 2007).
Thus, tongue/lip tie could be viewed as a potential causal factor for the breastfeeding challenges experienced by this group. However, between 1997 and 2012, the diagnosis of tongue/lip tie has increased more than 800% nationally (Walsh et al., 2017), and its diagnosis remains a controversial topic without clear agreement on best practices (Fraser et al., 2020;LeFort et al., 2021;Unger et al., 2020). Additionally, a Cochrane review of the effect of frenotomy on infant feeding found that performing frenotomy Recipients in this sample were largely using HMS as a strategy to supplement the mother's own milk, with the majority of recipients T A B L E 3 Breastfeeding experience and infant-feeding behaviours of study participants (n = 168), stratified by HMS donor/recipient status PEREGOY ET AL. | 9 of 13 still feeding their infants at the breast during the HMS arrangement.
Furthermore, the mean age at which the recipient children began consuming S-HM was 4.6 months, with a mean HMS participation duration of 3.3 months. Taken together, these data paint a picture of HMS among this sample as a temporary supplemental infant-feeding strategy for healthy, partially to predominantly breast milk-fed infants. However, this also means that 14% of infants were no longer receiving mother's milk when milk sharing occurred, and 29% were no longer feeding at their mother's breast. These findings suggest that there is a nontrivial faction of HMS recipients who were unable to overcome their breastfeeding difficulties and were likely in need of additional support. Unfortunately, to our knowledge, there are no other published studies with which to compare these findings.
It has been suggested that the emergence of HMS has negatively affected milk banks by competing for the same pool of eligible donors, thus reducing the supply of B-HM available for milk banks and neonatal intensive care units (Dutton, 2011;Jones, 2013;Newman, 2011;Rochman, 2011 to be similar to that of the E-HM that mothers are feeding to their own children. Indeed, a recent study analysed samples of S-HM, B-HM and E-HM expressed for a mother's own infant and found no difference in the rates of total aerobic bacterial or coliform growth, lysozyme activity, sIgA activity, lactose, fat, protein or water content between the samples (Perrin et al., 2018). Taken together, these findings suggest that, although mothers may not consistently follow HM handling and storage guidelines (Carre et al., 2018;Reyes-Foster et al., 2017), the quality of S-HM may be similar to that of E-HM that mothers are feeding their own infants.

| Strengths and limitations
This study has several notable strengths. The development of the survey tool was informed by the findings of a detailed ethnographic study with HMS recipients, resulting in a survey tool closely aligned with the lived experiences of milk-sharing parents. The survey tool was then subjected to two rounds of cognitive testing and refinement to ensure its construct validity. Another strength is the highly detailed survey tool, which covered a range of experiences and behaviours. Thus, the survey tool is the core strength of this study.
Additionally, sampling was conducted using various outreach methods to ensure that both online and community-based HMS participants were adequately represented in this study.
There are several limitations to this study. The use of nonrandom sampling techniques introduced potential bias into the sample. Our reliance on online recruitment strategies likely underrepresented HMS parents who do not use the internet to connect with other parents. Therefore, the data from this survey cannot be extrapolated to the general population of milk-sharing parents. Furthermore, because the survey was limited to HMS participants in the DMV region, these findings are limited in their generalizability to other geographic settings. The study inclusion criterion of having milk shared within the past 18 months introduces the potential for recall bias among parents who milk shared many months previously, likely during a stressful and sleep-deprived period in their lives. However, this was minimized in our study because 74% of respondents had T A B L E 4 (Continued) Recipients (n = 70) Donors (n = 98) Total (n = 168) Milk-sharing practice N % N % N % Child was receiving mother's own milk while milk sharing a 59 85.5 ----Child was still feeding at the mother's breast during part or all of milk-sharing arrangement a 49 71.0 ---- Abbreviations: BF, breastfeeding; E-HM, expressed human milk; EOF, Eats on Feets; HM, human milk; HM4HB, Human Milk 4 Human Babies; HMS, human milk sharing; S-HM, shared human milk. a Statistical testing was not conducted due to small cell sizes or lack of a comparison group.
*p < 0.05; **p < 0.0001. milk shared in the 9 months before taking the survey. Finally, the sample size of this study limited our ability to test for statistical differences in less commonly reported HMS practices.

| CONCLUSION
This study adds to the body of knowledge of milk sharing by describing the infant-feeding behaviours and milk-sharing practices among a US network of milk-sharing parents in detail and identifying important differences and similarities between HMS donors and recipients. We found that overall, HMS participants are achieving a long duration of lactation and HM feeding and, although not sociodemographically different, donors and recipients differed significantly in their maternal experiences and some infant-feeding behaviours. Many HMS recipients encountered compounded medical and mental health challenges, and thus represent a vulnerable population in need of additional psychosocial and lactation support to improve their mental health and breastfeeding outcomes.
Additional research is needed to further elucidate how HM sharing is incorporated into and modifies broader infant-feeding patterns.